Evaluation of Adsorbed Polyampholyte Layers by Using Quartz Crystal Microbalance

摘要

Viscoelastic properties of layers of polyampholytes adsorbed on charged surfaces were studied by quartz microgravimetry. By applying the Voigt viscoelastic model the effective mass and thickness of layers after adsorption from solution at different salt concentrations were calculated. The obtained results were compared with the Sauerbrey equation, which applies to the case of thin, rigid adsorbed layers. The estimates of mass and thickness from the Voigt model were typically larger, and were more strongly affected by variations in the ionic strength of adsorbing solution. Since the Voigt model uses multiple frequencies and dissipation overtones, it was found that the calculated adsorbed layer mass was closer to the actual values, while the Sauerbrey approach resulted in underestimation. This observation was explained by the fact that adsorbed layers of polyampholytes were soft and highly dissipative. It was noted that the observed changes in dissipation of the adsorbed polyampholyte layers were comparatively large, which suggests a large amount of coupled water.